An analysis of risk factors for the prediction of shoulder dystocia in 16,471 consecutive births.

This paper is a univariate analysis of the demographic, antepartum and intrapartum risk factors in a series of 16,471 consecutive deliveries in a tertiary obstetric and gynaecological unit in Singapore. In total, 12,229 term vaginal cephalic deliveries with 77 cases of shoulder dystocia were entered into the study for analysis. The incidence of shoulder dystocia was found to be 0.63% of all term vaginal cephalic deliveries. There is a direct relationship between increasing infant birthweight and incidence of shoulder dystocia. The critical birthweight for the prediction of shoulder dystocia is 3600 g. In order of decreasing relative risks, the factors which appear to be predictive of shoulder dystocia are a birthweight in excess of 3600 g, diabetes in pregnancy, lower social class, of Indian origin, maternal weight in excess of 70 kg, parity more than 4, and the use of oxytocics during labour. The local birthweight distribution is very different from the West. A policy for elective caesarean section for birthweights in excess of 4000 g (97% tile) would prevent 44% of shoulder dystocias, increase the caesarean section rate by 2% and half the perinatal mortality among births with shoulder dystocia.